The present invention represents an improvement over prior art methods and apparatus for removing excess ceramic slurry from organic foam by passing slurry-impregnated foam through one or more pairs of preset rollers. Such organic foam, which is typically polyurethane foam, serves as a matrix for ceramic material in the manufacture of filters for molten metals, such as aluminum metal.
Prior art methods and apparatus for removing excess ceramic slurry from organic foam are disclosed in Yarwood et al U.S. Pat. No. 4,075,303 and in Dore et al U.S. Pat. No. 4,024,212. Both patents specify a method wherein excess slurry is expelled by passing the foam at least twice through pairs of preset rollers to effect temporary compression. While these patents recognize the necessity for maintaining a uniform distribution of slurry through the foam upon release of compression, it has been found in practice that it is difficult to avoid a core effect (excess slip remaining in a central portion of the foam) after impregnated foam is passed through preset rollers only once or twice. Multiple passes through the rollers are required to obtain foams suitable for manufacturing adequate filters using the methods of these prior art patents.
It is a principal object of the present invention to provide a method and apparatus for removing excess ceramic slurry from a slurry-impregnated organic foam, wherein ceramic material is uniformly distributed throughout the organic foam.
It is a related object of the present invention to avoid the core effect which has plagued prior art methods and apparatus for removing excess slurry from organic foam.
It is an advantage of the present invention that a uniform distribution of ceramic material can be obtained in an organic foam by performing only a single operation, without multiple passes through preset rollers.
Additional objects and advantages of the present invention will become apparent to persons skilled in the art from the following specification, read in conjunction with the drawings.